Sequences are a handy feature in SQL server which provide an increasing, unique number. You wouldn’t typically use them directly but might use them under the covers in an identity. However from time to time they are useful when you need numbers but your primary key is a uniqueidentifier or you need two different ways of numbering records. I’ve been using them to associate records in a table into groups.

create SEQUENCE Seq_PermitNumber 
    start with 1 
    increment by 1

You can then use them like this

update tblManualPayment 
   set PermitNumber = next value for Seq_PermitNumber 
 where PermitNumber is null

This will give each record a unique permit number.